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  6. 2025 ICD-10-CM Code R99
Version 2025
Billable Code
No Valid Principal Dx
Convert to ICD-9

2025 ICD-10-CM Diagnosis Code R99

Ill-defined and unknown cause of mortality

ICD-10-CM Code:
R99
ICD-10 Code for:
Ill-defined and unknown cause of mortality
Is Billable?
Yes - Valid for Submission
Chronic Condition Indicator: [1]
Not chronic
Code Navigator:

R99 is a billable diagnosis code used to specify a medical diagnosis of ill-defined and unknown cause of mortality. The code is valid during the current fiscal year for the submission of HIPAA-covered transactions from October 01, 2024 through September 30, 2025.

According to ICD-10-CM guidelines this code should not to be used as a principal diagnosis code when a related definitive diagnosis has been established.

Code Classification

  • Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified
    (R00–R99)
    • Ill-defined and unknown cause of mortality
      (R99)
      • Ill-defined and unknown cause of mortality
        (R99)

Approximate Synonyms

The following clinical terms are approximate synonyms or lay terms that might be used to identify the correct diagnosis code:

  • Accidental death
  • Accidental death
  • Accidental death
  • Accidental death
  • Accidental death
  • Accidental death
  • Accidental death in home
  • Accidental death in industrial place
  • Accidental death in public place
  • Accidentally killed
  • Adverse incident outcome categories
  • Adverse incident resulting in death
  • Anesthetic death
  • Anesthetic death
  • Antepartum maternal death
  • Autopsy pending
  • Autopsy performed
  • Child death
  • Dead
  • Dead - death without witness
  • Dead - expected
  • Dead - sudden death
  • Dead - sudden death
  • Dead - suspicious death
  • Dead - unexpected
  • Dead on arrival at hospital
  • Death
  • Death associated with influenza
  • Death associated with respiratory syncytial virus infection
  • Death by asphyxiation
  • Death by fire
  • Death by hanging
  • Death by immolation
  • Death due to chemotherapy toxicity
  • Death due to radiotherapy toxicity
  • Death due to trampling
  • Death during anesthetic induction
  • Death from direct obstetric cause occurring more than 42 days but less than one year after delivery
  • Death from indirect obstetric cause occurring more than 42 days but less than one year after delivery
  • Death from overwork
  • Death from sequela of direct obstetric cause
  • Death from sequela of indirect maternal cause
  • Death in home
  • Death in hospice
  • Death in hospital
  • Death in hospital
  • Death in hospital
  • Death in hospital-based emergency department
  • Death in hospital-based emergency department or outpatient department
  • Death in hospital-based outpatient department
  • Death in less than 24 hours from onset of symptoms
  • Death in long term care facility
  • Death in nursing home
  • Death in nursing home or long term care facility
  • Death of unknown cause
  • Death of unknown cause
  • Death unattended by physician
  • Died at home
  • Died during operation
  • Died in ambulance
  • Died in care home
  • Died in community hospital
  • Died in general practice premises
  • Died in hospice
  • Died in hospital
  • Died in hospital
  • Died in hospital
  • Died in learning disability unit
  • Died in mental health unit
  • Died in nursing home
  • Died in street
  • Died in usual place of residence
  • Died without sign of disease
  • Direct maternal death
  • Early neonatal death
  • ECOG performance status - grade 5
  • ECOG performance status finding
  • Fetal disorder due to maternal death
  • Found dead
  • Found dead at accident site
  • Found dead in bed
  • GRACILE syndrome
  • Iatrogenic death
  • Iatrogenic death
  • Indirect maternal death
  • Infant death
  • Instantaneous death
  • Intraoperative death
  • Intraoperative or immediately postoperative death in an ASA Class I patient
  • Intrapartum maternal death
  • Killed
  • Late maternal death
  • Late neonatal death
  • Maternal death
  • Maternal death
  • Maternal death
  • Maternal death
  • Maternal death - perinatal
  • Natural death
  • Natural death reportable to medicolegal authority
  • Natural death with probable cause suspected
  • Natural death with proved cause
  • Natural death with proved cause by autopsy
  • Natural death with proved cause without autopsy
  • Natural death with unknown cause
  • Neonatal death
  • Non-traffic vehicular accidental death
  • Patient death associated with a fall while being cared for in a healthcare facility
  • Patient death or serious disability associated with a burn incurred from any source while being cared for in a healthcare facility
  • Patient death or serious disability associated with an electric shock while being cared for in a healthcare facility
  • Patient death or serious disability associated with patient elopement for more than four hours
  • Patient death or serious disability associated with the use of contaminated drugs, devices, or biologics provided by the healthcare facility
  • Patient death or serious disability associated with the use of restraints or bedrails while being cared for in a healthcare facility
  • Patient death or serious disability associated with the use or function of a device in patient care, in which the device is used or functions other than as intended
  • Patient deceased during stay
  • Patient status determination, deceased
  • Patient status determination, deceased and body cremated
  • Patient status determination, deceased and body donated
  • Patient status determination, deceased and buried
  • Patient status determination, deceased and entombed
  • Patient status determination, deceased and removed from state
  • Perinatal death
  • Perioperative death
  • Postmortem plain X-ray abnormal
  • Postmortem rigidity
  • Postneonatal death
  • Postoperative death
  • Postpartum maternal death
  • Postpartum maternal death
  • Preoperative anesthetic death
  • Serious reportable event associated with environment
  • Serious reportable event associated with environment
  • Serious reportable event associated with environment
  • Serious reportable event associated with environment
  • Serious reportable event associated with patient protection
  • Serious reportable event associated with product or device
  • Serious reportable event associated with product or device
  • Sudden death
  • Sudden death
  • Sudden death of unknown cause during the puerperium
  • Sudden death, cause unknown
  • Sudden death, cause unknown
  • Sudden infant death
  • Sudden infant death syndrome
  • Sudden infant death syndrome
  • Sudden infant death with dysgenesis of testes syndrome
  • Sudden unexpected death in epilepsy
  • Suspicious death
  • Traffic vehicular accidental death
  • Unattended death
  • Unattended death of unknown cause
  • Undetermined manner of death
  • Undetermined manner of death, natural causes suspected
  • Undetermined manner of death, suicide suspected
  • Unexpected death
  • Unexpected sudden death of adult
  • Unexplained sudden death

Clinical Classification

Clinical Classifications group individual ICD-10-CM diagnosis codes into broader, clinically meaningful categories. These categories help simplify complex data by organizing related conditions under common clinical themes.

They are especially useful for data analysis, reporting, and clinical decision-making. Even when diagnosis codes differ, similar conditions can be grouped together based on their clinical relevance. Each category is assigned a unique CCSR code that represents a specific clinical concept, often tied to a body system or medical specialty.

Other general signs and symptoms

CCSR Code: SYM016

Inpatient Default: Y - Yes, default inpatient assignment for principal diagnosis or first-listed diagnosis.

Outpatient Default: Y - Yes, default outpatient assignment for principal diagnosis or first-listed diagnosis.

Clinical Information

  • Sudden Infant Death

    the abrupt and unexplained death of an apparently healthy infant under one year of age, remaining unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history. (pediatr pathol 1991 sep-oct;11(5):677-84)

  • Perinatal Death

    the death of a fetus of gestational age 28 weeks or more, or the death of a live-born infant less than 28 days of age.

  • Infant Death

    the death of a live-born infant within its first year of life.

  • Maternal Death

    the death of the female parent.

  • Sudden Unexpected Death in Epilepsy

    sudden death in a patient with epilepsy associated with seizures and seizure-related symptoms (e.g., apnea; hypoxemia) without other identifiable accidental causes (e.g., drowning; wounds and injuries).

  • Infant

    a child between 1 and 23 months of age.

  • Direct Maternal Death

    death resulting from conditions or complications which are unique to pregnancy and occur during the antepartum, intrapartum, or postpartum period.

  • Indirect Maternal Death

    death resulting from previously existing disease or a disease developing during pregnancy which was not associated with gestation, but which was aggravated by the unique physiologic changes of pregnancy. examples of indirect deaths include those associated with epilepsy, diabetes, cardiac disease and hormone-dependent malignancies.

Tabular List of Diseases and Injuries

The following annotation back-references are applicable to this diagnosis code. The Tabular List of Diseases and Injuries is a list of ICD-10-CM codes, organized "head to toe" into chapters and sections with coding notes and guidance for inclusions, exclusions, descriptions and more.


Inclusion Terms

Inclusion Terms
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
  • Death (unexplained) NOS
  • Unspecified cause of mortality

Index to Diseases and Injuries References

The following annotation back-references for this diagnosis code are found in the injuries and diseases index. The Index to Diseases and Injuries is an alphabetical listing of medical terms, with each term mapped to one or more ICD-10-CM code(s).

Convert R99 to ICD-9-CM

  • ICD-9-CM Code: 798.0 - Sudden infant death synd
    Approximate Flag - The approximate mapping means there is not an exact match between the ICD-10 and ICD-9 codes and the mapped code is not a precise representation of the original code.
  • ICD-9-CM Code: 799.9 - Unkn cause morb/mort NEC
    Approximate Flag - The approximate mapping means there is not an exact match between the ICD-10 and ICD-9 codes and the mapped code is not a precise representation of the original code.

Code History

  • FY 2024 - No Change, effective from 10/1/2023 through 9/30/2024
  • FY 2023 - No Change, effective from 10/1/2022 through 9/30/2023
  • FY 2022 - No Change, effective from 10/1/2021 through 9/30/2022
  • FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016. This was the first year ICD-10-CM was implemented into the HIPAA code set.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.